Part 3 of a series arguing that preemptive RTOSes are often unnecessary for embedded systems. It surveys four lightweight cooperative schedulers — Protothreads, ULWOS2, cocoOS, and SST0/QV — comparing their features, thread-safety, and complexity. The second half shows how to extend the 'Superduperloop' scheduler with DIY inter-process communication: thread flags, binary semaphores, event flags, and timer notifications, all in a few dozen lines of C code. The result achieves RTOS-level worst-case response time while avoiding race conditions and keeping the codebase auditable.
